High throughput method and apparatus for measuring multiple optical properties of a liquid sample

ABSTRACT

An apparatus for the high throughput measurement of optical properties of liquid samples placed into the wells of a multiwell plate is disclosed. An optical fiber within a fiber bundle containing no corrective optics between the fiber ends and the well plate bottom illuminates the sample in order to induce fluorescence, and multiple fibers collect emission radiation and transmit it to a fluorescence detector such as a spectrometer. Other embodiments involve a light scattering illumination source with detection fibers located in either the same bundle containing the fluorescence monitoring fibers or an independent light scattering detection bundle for the measurement of static and/or dynamic light scattering. Some embodiments of the invention permit the measurement of phase analysis light scattering. Thus the measurement of multiple optical properties of a liquid sample may be made simultaneously or in succession. A method for these measurements is also disclosed.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.16/681,805, filed Nov. 12, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/583,899, filed May 1, 2017.

RELATED APPLICATIONS AND PATENTS

The following patents relate to the measurement of the physicalproperties of liquid samples in a multiwell plate and are herebyincorporated by reference:

-   U.S. Pat. No. 6,519,032 B1, S. C. Kuebler and J. Bennett, “Fiber    optic apparatus and use thereof in combinatorial material science,”    issued Feb. 11, 2003.-   U.S. Pat. No. 6,819,420 B2, S. C. Kuebler and J. Bennett, “Fiber    optic apparatus and use thereof in combinatorial material science,”    issued Nov. 16, 2004.-   U.S. Pat. No. 8,976,353 B2, M. I. Larkin, A. D. Hanlon, D. I.    Some, R. J. Sleiman, D. N. Villalpando, “Mutiwell plate lid for    improved optical measurements,” issued Mar. 10, 2015.-   U.S. Pat. No. 9,347,869 B2, M. I. Larkin, A. D. Hanlon, D. I.    Some, R. J. Sleiman, D. N. Villalpando, “Mutiwell plate lid for    improved optical measurements,” issued May 24, 2016.-   U.S. Pat. No. 9,459,207 B2, A. D. Hanlon, M. I. Larkin, “Method of    characterizing interactions and screening for effectors,” issued May    24, 2016.-   U.S. Pat. No. 8,441,638 B2, H.-T. Hsieh, S. P. Trainoff, “Apparatus    to measure particle mobility in solution with scattered and    unscattered light,” issued May 14, 2013.

BACKGROUND

Although the present disclosure will refer to particles throughout muchof its specification, the invention includes more generally all classesof small particles including emulsions, macromolecules, viruses,nanoparticles, liposomes, macro-ions and any other solution constituentswhose size may lie between a half and a few thousand nanometers. Thuswhenever the terms “particle,” “macromolecule,” or “macro-ion” are used,it should be understood they include all of the aforementionedsolution-borne objects. The present invention generally involves thecharacterization of particles and molecules in a liquid sample, and inparticular the measurement of fluorescence and light scattering ofsamples contained within the wells of a multiwell plate. Methods capableof measuring samples directly in these multiwell plates are generallydesirable given both the high-throughput nature of the measurementspermitting the rapid screening of the individual samples, as well as thereduced sample volume requirements. Standard multiwell plates have 96,384, or 1536 wells, each well is able to contain a different sample, andall wells, under common operational conditions, may be tested in asingle data collection run. In addition, use of these plates obviatesthe laborious need to clean and dry individual scintillation vials aftereach measurement. These plates generally have very low volume wells, andcommercially available multiwell plate based measurement instruments arecapable of measurements from sample volumes of 1 μL or less. These tinysample volumes are of great benefit when one has a limited amount ofsample from which to make measurements, particularly when compared tothe 300 μL or larger sized measurement volumes often required by othermeasurement techniques, such as flow-through fluorescence monitoring andflow-through multiangle light scattering (MALS). Other obvious benefitsinclude the ability to automate the measurement of between 1 and over1500 samples with little or no human intervention after the sample isprepared and introduced into the plate for analysis. Further laborsaving benefits can be achieved, of course, by automated samplepreparation robots such as the Freedom EVO® series produced by Tecan(Tecan Trading AG, Switzerland).

Multiwell plates can be used with various optical analysis techniques,most commonly absorbance measurements performed as light is scannedacross a plate and the transmitted light is measured by a detectorsystem placed on the opposite side of the plate to the incident light,permitting, thereby a measurement of the absorbance of light by thesample contained in each individual well as described, for example, byA. J. Russell and C. Calvert in U.S. Pat. No. 4,810,096 (Issued Mar. 7,1989). Measurements of absorbance can enable a calculation of theconcentration of the sample contained therein.

Light scattering measurements may also be performed in a multiwell plateas described by Kuebler, et. al., in U.S. Pat. No. 6,519,032 B1 (issuedFeb. 11, 2003). In this technique a fine beam of light, generallyproduced by a laser, is directed to pass vertically through the samplecontained in a single well (either from above or below), and scatteredlight is detected by a detector located beneath the sample well. Theapparatus disclosed by Kuebler utilizes a technique generally referredto as dynamic light scattering (DLS) that is also known as quasi-elasticlight scattering (QELS) and photon correlation spectroscopy (PCS). Whenin solution, sample particles are buffeted by the solvent molecules.This leads to a random motion of the particles called Brownian motion.As light scatters from the moving particles this random motion imparts arandomness to the phase of the scattered light, such that when thescattered light from two or more particles is combined a changingintensity of such scattered light due to interference effects willoccur. The DLS measurement of the time-dependent fluctuations in thescattered light is achieved by a fast photon counter, generallyconnected by an optical fiber to collection optics located beneath themultiwell plate. The fluctuations are directly related to the rate ofdiffusion of the particles through the solvent. The fluctuations arethen analyzed to yield diffusion coefficients and, from these, thehydrodynamic radii of the sample.

Another measurement of interest, which is a focus of the presentinvention, is the detection of fluorescence from particles containedwithin the liquid sample. In general fluorescence studies involvetreating particles, such as chromosomes or proteins with a fluorescencetag or dye. The sample is then irradiated with an excitation lightsource, the protein tags are excited, causing electrons to rise to ahigher energy state, when the electrons from the tagged proteins returnto their ground state, they emit photons of a longer wavelength that canbe captured by an optical detector, such as a photomultiplier tube(PMT), and analyzed, and thus the tagged proteins can be identified andcharacterized. Often the spectrum of the fluorescence is measured foreven richer information content. Some molecules, most notably proteins,possess intrinsic fluorophores and can be excited with proper lightsources. For example, UV light at 280 nm excites both tyrosine andtryptophan residues, while 295 nm light excites only fluorescence fromtryptophan residues. Intrinsic protein fluorescence spectrum can be usedto assess the tertiary protein structure as the fluorescence peak tendsto red-shift as the residues are exposed to more polar environment. Themeasurement of protein free energy of unfolding can be determined bycombining chemical denaturation, generally using urea or guanidinehydrochloride, with measurement of intrinsic fluorescence. The proteinfree energy of unfolding is an indicator of formulations stability.

Many systems have been developed to measure fluorescence of a samplematerials, including directly from animal tissue, lab-on-a-chiptechnologies, or measuring fluorescence-labeled target moleculesimmobilized on a solid support. Significantly fewer developments havebeen concerned with fluorescence studies of liquid samples contained ina multiwell plate, although some patents have explored improvements tothe collection of fluorescence data of samples contained therein. Forexample, U.S. Pat. No. 6,316,774 discloses a fluorimeter where lightpasses from the source through one of two optical fibers, the selectionof which is controlled manually. These fibers permit illumination of thesample contained within a plate or cuvette either through the open topof the chamber or through the transparent closed bottom by reflectingthe incoming light from the fiber with a concave, focusing mirror thatdirects the illumination to the sample chamber. Additional collectingmirrors and optics gather the emission radiation and direct it intooptical fibers that carry the light to an optical shutter that permitspassage from emitted light gathered either from above or below thesample plate.

Combined illumination and collection optics have been subject of otherfluorimetry innovations. U.S. Patent Application No. US 2010/0032582 A1(published Feb. 11, 2010) by H. Xia, et. al. utilizes a single opticalfiber bundle comprising a central illumination fiber surrounded with aplurality of receiving fibers contained within a single bundle, andutilizing a single lens to direct the paths of both the excitationradiation to the sample and receipt of the emission radiation from thesample that is contained within a microfluidic channel. Similarly U.S.Pat. No. 4,678,326 (Issued Jul. 7, 1987) by H. Harjunmaa proposes abundle of fibers with an emission fiber in the center and utilizing apair of lenses to collimate excitation radiation through the bottom ofcylindrical cuvette in order to avoid illumination of the cuvette wallsby the incident light while maximizing the uniformity of illumination ofthe sample. The same lens configuration collects light emitted from thesample and directs it into a plurality of fibers arranged at specificradial distances surrounding the emission fiber selected so as to rejectreflected light from the bottom surface of the cuvette.

In addition to these systems for measuring fluorescence from a multiwellplate, improvements to the optics and light collection and rejectionsystems have also been considered and are present in the prior art. Forexample U.S. Pat. No. 7,595,881 by S. W. Leonard, et. al, discloses auseful optical system wherein a shadow disc is placed within the path ofemission radiation collected and directed, in free space, by a mirrorlocated below the well plate. By careful positioning and alignment ofthe optical elements, the shadow disc absorbs light scattered by themeniscus of the sample cell, the remaining radiation is then focusedwith an aspheric lens onto a detector, improving the overallsignal-to-noise of the collected light.

While all of these implementations offer significant improvements overfundamental fluorimeter systems, it is not until the present inventionthat a simplified system that maximizes the signal to noise ratio whileminimizing stray light and permitting the high-throughput analysisenabled by multiwell plates has been possible.

A BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a typical instrument for measuring fluorescence of a liquidsample contained within a cuvette.

FIG. 2 illustrates a variation on the conventional fluorimeter shown inFIG. 1 wherein optical fibers are used to direct light to and collectinglight from a liquid sample.

FIG. 3A shows an embodiment of the present invention wherein a singleprobe contains fibers that transmit the excitation beam and collectemission radiation from a sample contained in a multiwell plate. FIG. 3Bexhibits a close up view of the probe barrel.

FIG. 4A is a detailed view of the excitation and emission radiationtransmitted from and collected by the probe. FIG. 4B shows a preferredembodiment of the probe barrel which is beveled such that thefluorescence excitation/probe barrel may be brought as close to theplate bottom as possible.

FIG. 5 shows a preferred embodiment of the invention wherein two fiberbundle probes act in concert to collect fluorescence and lightscattering signals from the liquid sample located in the well of amultiwell plate.

A DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a conventional fluorimeter 100 for use with a liquidsample. An illumination source 101, which can either operate at aspecifically chosen excitation wavelength, or over a range of possiblewavelengths, generates a beam of light selected by an aperture and isgenerally collimated by a lens 102. The collimated beam may then passthrough an optical filter 103 that permits the passage of a specificallyselected excitation wavelength, λ₁, or range of wavelengths of radiationto pass there through. The excitation beam 109 is then directed towardsthe liquid sample 110 by a dichroic beam splitter 104 that reflectslight at wavelength λ₁. The excitation beam then generally passesthrough a lens 105 that focuses the beam 109 to a point 106 somewherewithin the liquid sample 110 contained within the sample vessel 111. Theexcitation beam 109 then exits the sample through the sample meniscus107. The emerging beam may then intersect an optical detector 108 thatmeasures the amount of light transmitted through the sample. Asdiscussed above, the excitation beam may cause various molecules withinthe liquid sample to fluoresce at a wavelength λ₂, where λ₁<λ₂. Thefluorescent light that emerges from the bottom of the sample vessel 111is collected and collimated by a lens 105 forming an emission beam 112.The emission beam 112 impinges upon the dichroic beam splitter 104 thathas been selected to transmit, rather than reflect or absorb, atemission wavelength λ₂. The emission beam is then focused by aconverging lens 113 which directs the beam towards a detector 114 whichis generally a photomultiplier tube (PMT) or an avalanche photodiode(APD). It is also not uncommon for the dichroic beam splitter 104 topermit the passage of a percentage of light from the excitation beam 109to pass there through and impinge upon a photodetector (not shown). Whenthe intensity of light gathered by this detector is compared with thelight gathered by the optical detector 108 located above the sample, itis possible to determine the absorption of light by the sample itself,broadening, thereby the utility of the system.

A variation on a conventional fluorimeter employs fiber optics for thedelivery of excitation radiation as well as the collection of emissionradiation, an example of such a system is illustrated in FIG. 2 . Thelight source 101 of FIG. 1 can be replaced by a single wavelength lightemitting diode (LED) or a UV laser source. In this case the opticalfilter 103 may be eliminated from the optical system as LEDs and lasersources generally operate at very narrow wavelength bands, and the LEDor laser source would be selected to operate at the desired excitationwavelength. In this case, the LED source 201 is focused by a converginglens 202 onto one end of an optical fiber 203. In this specification werefer to this end of the fiber as the system end. By contrast the end ofthe fiber directly investigating the sample is referred to as the probeend. The excitation light passes through the fiber 203 and the emergingbeam 204, at the probe end, may be expanded by a lens 205 such that thebeam illuminates a large volume of the sample 206 contained in thevessel 207. Emission radiation leaving the vessel 207 can be gathered bya converging lens 208 and focused onto a second optical fiber 209 afterpassing through an optical filter 210 selected to allow only light ofthe expected emission wavelength to pass there through. The emissionbeam 211, after passing through the fiber 209 can be focused onto adetector 212 such as a PMT or APD by a converging lens 213. It is alsopossible to remove the attenuator, and rather than detect absoluteluminosity, the spectrum of emitted radiation can be analyzed byreplacing the detector 212 with a spectrometer. Further, the excitationsource may employ multiple LEDs emitting light at multiple wavelengths,and then selecting from among those wavelengths one or more of the LEDsto illuminate the sample in order to optimize the determination ofexcitation wavelengths. Similarly, wide spectrum sources can be used inconjunction with filters which are selected to permit the passage of asingle wavelength, the filtered beam is then focused on the excitationfiber 203 rather than using a narrow wavelength LED source.

Several embodiments of the present invention comprise a novel means oftransmitting excitation radiation to a liquid sample contained within amultiwell plate and receiving emission radiation therefrom. FIG. 3illustrates one embodiment of the invention. The wells 302 of amultiwell plate 301 each contain a liquid sample 303 comprisingfluorescently tagged or intrinsically fluorescent samples of interest.The bottom portion of the multiwell plate is transparent at least in aregion directly below each of the wells. The remaining surfaces of theplate may be optically transparent, but in a preferred embodiment, thenon-beam passing surfaces will absorb light at the wavelengths of eitherthe excitation source or the emission wavelength or both. An opticalprobe 305 is located on a stage beneath the multiwell plate 301 wherethe stage may be a translation device capable of movement in at least Xand Y directions relative to the multiwell plate positioned there above,allowing the probe 305 optical access to each of the wells individuallyby moving either the probe or the multiwell plate itself. Throughoutthis specification the terms “stage” and “translation device” indicatean object to which the probe or probes are mechanically attached.Neither term limits the invention to an embodiment wherein theprobe/probes or multiwell plate is the moving element. The probecomprises a plurality of optical fibers wherein one or more of thefibers is an excitation radiation delivery vehicle capable of deliveringa narrow-band light source, a broad-band light source, or a multitude oflight sources. A plurality of remaining fibers collects emissionradiation from the illuminated sample. In a preferred embodiment shownin FIG. 3 , the excitation source is a LED with a center wavelength λ₁.The light from the LED is transmitted through a fiber 304 located at thecenter of the bundle of fibers which is contained in the probe barrel305, as can be seen in FIG. 3B. A plurality of emission collectionfibers 306 are arranged about the excitation fiber 304. The number ofcollection fibers 304 can range from one to any practical limit dictatedby the size of the probe barrel 305 and possible orientations. In apreferred embodiment the number of excitation fibers is chosen tomaximize the light gathering efficiency and detection signal to noiseratio. In contrast to the prior art discussed above, the presentinvention does not make use of any additional light gathering opticsbetween the fibers themselves and bottom of the well plate. Thisconspicuous absence of transmission and gathering optics offers thenovel advantages of minimizing the number of interfaces traversed by theexcitation beam and emitted light. This drastically reduces stray lightfrom excitation light scattering at the interfaces. Coupled with aslight tilt (θ=10°˜20°) between the probe barrel 305 and the platebottom normal, the stray light from excitation source can be reduced tosuch a level that the excitation blocking filter at the detector is nolonger necessary. As a result the excitation fiber 304 is able toilluminate the sample in a controlled and consistent manner as it movesfrom well to well. In addition each of the emission radiation receivingfibers collects based on the positioning of the fibers within the faceof the barrel, not based on the optics of a light gathering objectivelens. Of course, this novel probe also reduces cost and alignment timeassociated with an objective lens (or lenses) otherwise contained withinthe barrel of the probe or otherwise situated between the probe and thewell plate itself.

In one embodiment of the invention, the excitation sources is a LED 307operating at a wavelength selected so as to excite atoms of moleculescontained within the sample. The light from the LED 307 is delivered atthe probe end with the emission radiation gathering fibers 306 in theprobe barrel 305. The fiber bundle is bifurcated with the illuminationfiber or fibers coupled to the light sources and the emission fibers 306splitting off from the bundle to be directed to a light sensitivedetector or a spectrometer 308. In one preferred embodiment the emissiongathering fibers on the system end are arranged into a linear array,permitting thereby the maximum amount of gathered emission light to passthrough a linear slit 309 at the entrance of a detector such as aspectrometer 308.

The probe barrel 305 containing the probe ends of both the excitation304 and collection fibers 306 is positioned at an angle θ normal to thebottom of the plate. This configuration minimizes back reflection fromthe bottom surface of the well plate. FIG. 4A shows an excitation beamdelivered by the excitation fiber 401 and emission from the sample 402is collected by collection fibers 404. In a preferred embodiment of theinvention, a cross section of which is shown if FIG. 4B, the barrel 403b is beveled and the contained fibers are both beveled and polished atan angle of around θ+90°, such that the flat surface of the barrel isessentially parallel to the bottom of the multiwell plate 405. Thispreferred embodiment enables both the probe to be placed much closer tothe bottom of the multiwell plate 405, where distance d′ between theface of the beveled barrel and the bottom of the multiwell plate is muchsmaller than the distance d between the plate and the center of thebarrel 403 a held at an angle, minimizing back-reflections from opticalinterfaces, particularly those that would be required if an objectivelens were used to shape and direct radiation, as is the case inconventional systems. This novel beveled barrel also allows the fibersto collect radiation passing normal through the bottom of the samplewell, as the faces of the fiber are polished flush to the beveled angle,and thus light exiting normal to the bottom face of the multiwell platewill pass directly into the probe.

In addition to the fluorescence detection discussed thus far in thisdisclosure, another embodiment of the invention enables the collectionof light scattering data from liquid sample contained in the samemultiwell plate. By using a second probe in conjunction with thatdiscussed previously, one may combine fluorescence detection with bothstatic light scattering (SLS) and dynamic light scattering (DLS) in asingle measurement instrument, capable of making a plurality ofmeasurements simultaneously or in succession from a multiwell plate,allowing a wealth of information to be acquired in a fraction of thetime conventionally necessary in a high throughput system. As shown inFIG. 5 , the beveled fluorescence probe of FIG. 4 may be accompanied bya separate optical fiber acting as an illumination source for lightscattering measurements. In a preferred embodiment of the invention thelight scattering illumination fiber will be a single-mode,polarization-maintaining fiber and the DLS detecting fiber can be asingle-mode or multi-mode fiber. In another preferred embodiment of theinvention, both the DLS and SLS fibers will have a diameter ofapproximately nine microns. Two of the fibers in the fluorescence probebundle will serve as SLS and DLS collection and transmission vehicles,permitting thereby measurements of light scattering at a fixed anglefrom the incident beam.

In certain circumstances corrective optics may enhance SLS and DLSdetection. While it is possible in some embodiments of the invention toattach corrective optics directly to the fibers to be utilized for lightscattering purposes, it is perhaps simpler to employ a third probededicated to light scattering detection which may house separate fibersfor the SLS and/or DLS detection. As such, another embodiment of theinvention comprises the elements shown in FIG. 5 as well as a thirdprobe housing containing corrective optics and one or more fiberscoupled to the DLS and/or SLS detectors. In this embodiment thefluorescence probe may be dedicated completely to excitation andemission detection or may still utilize one or more fibers coupled toindependent SLS or DLS detectors, permitting thereby light scatteringdata collected with and without corrective optics to be compared. Inthis embodiment the dedicated light scattering probe shares a singleoptical barrel and lens on one end and the system end is separated intothe individual or groups of fibers, such as the “fan-out” fiber opticbundles produced by Thorlabs (Newton, N.J.). The three detector probesin these embodiments, namely the fluorescence probe, light scatteringillumination probe, and light scattering detection probe may be rigidlycoupled to each other by means of a movable stage such that they mayinvestigate the same sample well of a multiwell plate simultaneously orwith optical investigations being performed in series, without the needto move the stage to which the probes are rigidly coupled, or to movethe multiwell plate relative to the stage. In another variation,fluorescence probe may be so positioned relative to the light scatteringillumination probe and light scattering detection probe that thefluorescence probe measures fluorescence of one sample while the lightscattering probes measure light scattering from a separate samplelocated within the same multiwell plate.

Under certain circumstances it may be required to adjust the height ofthe stage to which the probes are connected relative to the multiwellplate, therefore another variation enables the movement of the stagerelative to the plate along the z-axis as well as the x-y axes. Forexample, consider a multiwell plate wherein very small amounts of sampleare added to a plurality of wells, and therefore the well is onlypartially filled. It may be of interest to make a fluorescencemeasurement with the beveled fluorescence probe shown in FIG. 5 as closeas possible to the bottom of the multiwell plate, but as the lightscattering probe may be aligned such that it collects light scatteredfrom the mid height of the well. In this case, this embodiment permitsthe positioning of the fluorescence probe very close to the multiwellplate for a fluorescence measurement, and then the stage may be movedalong the z-axis away from the bottom of the plate, to allow thedetection of light scattering from sample nearer the bottom of the wellin order to avoid any noise associated with the meniscus of the liquidsample.

While much of this disclosure concerns the enablement of fluorescencedetection from a liquid sample in a multiwell plate, another embodimentof the invention is that described above but absent the fluorescenceprobe. In this embodiment there are only two probes, one is the lightscattering illumination source and the other houses corrective opticsand two or more fibers, at least one of which is coupled to a DLSdetector and at least one of which is coupled to an SLS detector.

Further, another embodiment of the invention permits the measurement ofelectrophoretic mobility of the liquid sample contained with a well byincorporating into the system a pair of electrodes, which may be eitherelements of a specialized well plate or elements of a plate lid thatcovers the plate, the electrodes connected thereto contacting the liquidsample. As discussed by Hsieh and Trainoff in U.S. Pat. No. 8,441,638B2, “Apparatus to measure particle mobility in solution with scatteredand unscattered light,” (Issued May 14, 2013) (the '638 patent), theelectrophoretic mobility is the directly measurable and most widely usedquantity which characterizes the electrostatic properties of themolecules, or for that matter any other particles present, in suchsolutions. In this embodiment a voltage is applied across theelectrodes, and charged particles within the sample migrate towards theoppositely charged electrode. The light scattering illumination beam issplit prior to entry into the well into a sample beam and a referencebeam. The sample beam passes through the liquid sample, but thereference beam does not, and is phase modulated by an external source,such as a piezo driven mirror as described in the '638 patent. Lightscattered from the sample exposed to the electric field is collected byone or more of the collection fibers and recombined with the referencebeam and the resulting beam is measured by a photodetector suchphotodiode. The signal from electrophoretic mobility detector is thenanalyzed to extract optical phase information, giving a first-principlemeasurement of the electrophoretic velocity of the macromolecules withinthe scattering volume.

As will be evident to those skilled in the arts of optical measurementsfrom liquid samples, the benefits conveyed by the present invention arefar reaching, and there are many obvious variations of the methods ofthe invention that do not depart from the fundamental elements thatdisclosed herein; all such variations are but obvious implementations ofthe described invention and are included by reference to our claims,that follow.

What is claimed is:
 1. An apparatus comprising: a multiwell platecomprising at least one vessel to contain a suspended liquid sample,wherein the at least one vessel comprises a transparent bottom surface;a primary optical fiber bundle comprising a probe end and a system end,wherein the primary optical fiber bundle comprises: at least oneillumination fiber optically coupled to an excitation radiation sourceon the system end of the primary optical fiber bundle and positioned toilluminate the suspended liquid sample on the probe end of the primaryoptical fiber bundle, and a plurality of collection fibers positioned,on the probe end of the primary optical fiber bundle, to collectradiation from the liquid sample illuminated by the at least oneillumination fiber and optically coupled, on the system end of theprimary optical fiber bundle, to at least one detector, wherein a chosenquantity of the at least one illumination fiber maximizes a lightgathering efficiency of the plurality of collection fibers and adetection signal to noise ratio of the plurality of collection fibers; atranslation device coupled to the probe end of the primary optical fiberbundle, wherein the translation device is to provide relative motionbetween the probe end of the primary optical fiber bundle and thetransparent bottom surface; wherein the plurality of collection fibersare arranged concentrically about the at least one illumination fiber onthe probe end of the primary optical fiber bundle; wherein the probe endof the primary optical fiber bundle is positioned at an angle to thebottom surface of the at least one vessel of the multiwell plate and inthe absence of additional light gathering optics between the primaryoptical fiber bundle and the bottom surface; wherein the translationdevice is to move the probe end of the primary optical fiber bundlealong x-, y-, and z-axes with respect to the transparent bottom surface;wherein the multiwell plate is stationary and the translation device isto move the probe end of the primary optical fiber bundle relative tothe multiwell plate; and wherein non-beam passing surfaces of the vesselabsorb light at wavelengths of the excitation radiation source.
 2. Theapparatus of claim 1 wherein the plurality of collection fibers, on thesystem end of the primary optical fiber bundle, are arranged in a lineararray, and further comprising a linear slit located between the lineararray and the at least one detector.
 3. The apparatus of claim 1 furthercomprising a light scattering detection optical fiber bundlemechanically coupled to the translation device, wherein the lightscattering detection optical fiber bundle comprises at least one opticalfiber comprising a probe end and a system end, wherein the at least oneoptical fiber of the light scattering detection optical fiber bundle isoriented so as to be able to collect light scattered from the sample byat least one of a light scattering illumination source and theexcitation radiation source on the probe end of the at least one opticalfiber and is optically coupled to at least one light scattering detectoron the system end of the at least one optical fiber.
 4. The apparatus ofclaim 3 wherein the light scattering illumination source is a laser. 5.The apparatus of claim 1 wherein at least one optical fiber of theprimary optical fiber bundle is optically coupled on the system end ofthe primary optical fiber bundle to a static light scattering detector.6. The apparatus of claim 1 wherein at least one optical fiber of theprimary optical fiber bundle is optically coupled on the system end ofthe primary optical fiber bundle to a dynamic light scattering detector.7. The apparatus of claim 1 wherein the at least one detector is afluorescence spectrometer.
 8. The apparatus of claim 1 wherein theexcitation radiation source is a variable wavelength source.
 9. Theapparatus of claim 1 wherein the excitation radiation source is a lightemitting diode.